Method of treating powdered metal



United States Patent NIETHOD 0F TREATING POWDERED METAL John M. Joyner, Winsted, Conn., assignor to Farrel-Birmingham Company, Incorporated, Ansonia, Conn., a corporation of Connecticut No Drawing. Application April 17, 1956 Serial No. 578,584

6 Claims. (Cl. 75-214) This invention relates to a method of treating powdered metal and more particularly to the formation of metal articles by compounding metal powders with a binder in order to give a certain degree of plasticity to the mass and, when the mass has been thoroughly mixed, working it in any one of a number of processes to a shape or approximate shape in which it is desired to be used, then sintering the piece thus formed to drive off the binder and render more dense the resulting metallic product.

It is becoming comparatively well known to form metal articles by employing the metal which may be an alloy of a number of metals in powdered form, and then, by applying pressure to the metal in any one of several ways, consolidate it or compress it into a desired form or shape. Also in some instances a binder has been employed to maintain the metal batch in a somewhat plastic form during the handling process prior to its consolidation and formation into a desired shape.

It is contemplated by the present invention to employ with the powdered metal a binder, which binder may be driven off by a sintering process. This binder, it has been found, may advantageously comprise rubber, either natural or synthetic.

The rubber is employed in uncured form and is thoroughly mixed with the quantity of metal powder. When thoroughly mixed with the powder the resulting material may be described as a stiff dough, and this may be advantageously worked and formed into any desired shape. Moreover, if the resulting product or formed piece is subjected to heat, the rubber will be driven off, leaving a product which may be further processed by hot or cold rolling or other working process to produce the required end product.

The employment of a plastic binder such as natural or synthetic rubber assists in the initial working of the body of material into the desired shape in that when pressure is applied to a mass of the metal and binder, this pressure will be transmitted laterally or transversely throughout the mass with respect to the direction of pressure so as to cause the metal to fiow around corners, so to speak, and completely fill voids if a piece of irregular shape is being formed.

Moreover, it has been found that the mass can be worked at a lower temperature than when resins are used as binders, and moreover when the rubber is thoroughly worked prior to use as a binder, it is quite inert to change of shape, and for that reason the mixed mass retains its shape after being formed and prior to sintering. Rubbers also have suitable flow characteristics so that a relatively small amount of binder may be employed to permit forming by extruding, rolling, swaging, or other working processes.

While in the present application the use of rubber is stressed as the primary binder, it will be understood that other additives in minor amounts may be used in addition to the rubber to effect plasticity or other changes in Patented Sept. 1, 1959 "ice the rubber which might be desired for the particular type of processing.

One object of the present invention is to provide a method of preparing from metal powders articles of any desired shape by the employment, with the metal powder, of a binder which will retain the metal powder readily workable into a desired form and shape.

Still another object of the invention is to provide a method for preparing articles of any desired shape from metallic powder or powders, using as a binder a plastic material such as natural or synthetic rubber in the uncured state.

A still further object of the invention is to provide a method of producing from metallic powders articles of any desired shape which may be readily worked or processed at relatively low temperatures as compared with prior methods used in such processes.

To these and other ends the invention consists in the novel features and combinations of steps to be hereinafter described and claimed.

In accordance with the present invention a mass having considerable plasticity is compounded by mixing metallic powder with the rubber binder. The powder may be one of a single metal such as iron, for example, or it may consist of powders of a number of metals which are to be alloyed together, the amount, of course, being used in the proper proportions suitable for the alloy described in the finished product. The metallic powder is compounded with the binder so as to produce a uniform homogeneous mixture.

This mixture may be performed in a mixing device such as the Well-known Banbury mixer, for example. The binder may be placed in the mixer and the proper amount of the metal powder added. The relative amounts of the metal and binder may be varied to some extent, depending upon the characteristics desired of the resulting mixed mass. For example, natural rubber has been compounded with powdered iron in various quantities, the amount of rubber being from 5 to 15 percent by weight of the total weight of the batch. The lower ranges in the above percentages appear to be more satisfactory than the higher as the latter showed greater porosity and less strength.

After the binder has been placed in the mixer and the metal powder added, the mixer is operated until a uniform homogeneous mixture is obtained. No heat is employed in this operation except that which is generated by the operation of the mixer itself, and usually this is cooled by the use of a cooling fluid. Natural raw rubber has been employed but other types of rubber such as synthetic rubber can be used. They will be employed in uncured state.

The batch, when thoroughly mixed, is removed from the mixer in lumps and may be described as being in the form of a stiff dough having considerable plasticity. These lumps of material may then be processed, and for this purpose are placed into a machine of the proper type to give the material its basic form. The material may be, for example, worked in a rolling mill if sheets are desired, or may be worked in a press, extruder or swaging device, such as a crusher, if other forms or shapes are de sired. These forming operations are also carried out without the addition of any heat, the only heat present being the increase in temperature accompanying the working of the material.

The pieces thus formed then pass to a sintering furnace where they are sintered and the powdered metal further consolidated and the binder driven off. This may be done in a continuous sinter furnace or may be effected as a batch. The temperature to which the material is subjected in this operation depends upon the material used, i.e., the metals of which the powder is composed, and the size of grain. This grain size is selected in the powder according to the end product desired.

The sintering temperature is, of course, below the melting point of the metal, and the sintering operation may be performed with or without the application of pressure. In either case further consolidation occurs.

The sintering operation is carried out in a controlled atmosphere which in the case of rubber may be an atmosphere of hydrogen so that the rubber decomposes and volatilizes. Thus the binder is sbstantially completely driven off, leaving the pieces of the metallic powder.

The basic product thus obtained may then be further processed depending upon the end product desired. It may be treated by hot or cold rolling, for example, or by other process to produce the desired shape. After such processing, if the required shape is not obtained, the product may be cut or formed into the final shape in any of the usual methods as it is found that metal formed by the above process may be subjected to any of the usual forming operations.

As one example of the above process, powdered iron has been compounded with natural rubber in varying percentages, the rubber being employed in from 5 to 15 percent of the total weight of the batch as previously stated. In one instance where a mixture of 94 percent iron and 6 percent of rubber by weight was employed, the resulting product was successfully extruded in an extrusion press of usual form. This, of course, could also be pressed in a mold or passed through a rolling mill or swaged in order to give it its basic form. This processing was, of course, performed after the rubber binder and metallic powder had been thoroughly mixed in a Banbury mixer. The rubber in this instance was natural rubber in its uncured state, but uncured synthetic rubbers could be employed with equally good results.

After processing, the pieces thus formed were sintered as described above in an atmosphere of hydrogen and the rubber decomposed and driven off, the sintering temperature being below the melting point of iron but sufficiently high to decompose and volatilize the rubber. The product was then used in some instances as it came from the sintering furnace, and it was found that it could also be rolled or otherwise worked into a desired shape or prodnet.

The term elastomer" is employed in this application in claims to refer to a natural or synthetic rubber, the latter being of the organic type such, for example, as the wellknown GRS or Butyl rubber.

While I have described some preferred embodiments of my invention, it is not to be limited to all of the details shown, but is capable of modification and variation within the spirit of the invention and the scope of the appended claims.

What I claim is:

1. The method of making a metallic article from powdered metal which comprises mixing the metallic powder with a binder of an uncured organic elastomer, without the addition of heat, in a mixing device having a bladed rotor, in the amounts of from to percent of the powder to 5 to 15 percent of the elastomer, continuing the mixing operation until a thorough mixture of the two substances is obtained which is plastic at ordinary temperatures, removing the mass from the mixing device and working such mass under pressure into a desired form, and then sintering the resulting product in a controlled atmosphere to decompose and drive off the elastomer binder.

2. The method of making a metallic article from powdered metal as set forth in claim 1 wherein the elastomer binder is natural uncured rubber.

3. The method of making a metallic article from powdered metal as set forth in claim 1 wherein the elastomer is natural uncured rubber, and the sintering is eifected at a temperature sufficiently high to decompose and volatilize the rubber but below the melting point of the metallic powder.

4. The method of making a metallic article from powdered metal which comprises mixing the metallic powder with a binder of an uncured organic elastomer, without the addition of heat, in a mixing device having a bladed rotor, in the amounts of from 85 to 95 percent of the powder to 5 to 15 percent of the elastomer, continuing the mixing operation until a thorough mixture of the two substances is obtained which is plastic at ordinary temperatures, removing the mass from the mixing device and cold working such mass under pressure into a desired form, and then sintering the resulting product in a controlled atmosphere to decompose and drive off the elastomer binder.

5. The method of making a metallic article from powdered metal as set forth in claim 4 wherein the metal is further worked after the sintering operation to produce the finished article.

6. The method of making a metallic article from powdered metal as set forth in claim 1 wherein the elastomer is natural uncured rubber and is thoroughly worked prior to being mixed with the metallic powder.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,943 Wainer Apr. 22, 1952 2,622,024 Gurnick et a1. Dec. 16, 1952 2,709,651 Gurnick et al May 31, 1955 2,819,163 Balke et al. Jan. 7, 1958 

1. THE METHOD OF MAKING A METALLIC ARTICLE FROM POWDERED METAL WHICH COMPRISES MIXING THE METALLIC POWDER WITH A BINDER OF AN UNCURED ORGANIC ELASTOMER, WITHOUT THE ADDITION OF HEAT, IN A MIXING DEVICE HAVING A BLADED ROTOR, IN THE AMOUNTS OF FROM 85 TO 95 PERCENT OF THE POWDER TO 5 TO 15 PERCENT OF THE ELASTOMER, CONTINUING THE MIXING OPERATION UNTIL A THOROUGH MIXTURE OF THE TWO SUBSTANCES IS OBTAINED WHICH IS PLASTIC AT ORDINARY TEMPERATURES, REMOVING THE MASS FROM THE MIXING DEVICE AND WORKING SUCH MASS UNDER PRESSURE INTO A DESIRED FORM, AND THEN SINTERING THE RESULTING PRODUCT IN A CONTROLLED ATMOSPHERE TO DECOMPOSE AND DRIVE OFF THE ELASTOMER BINDER. 